i'm not sure exactly what's my version, eclispe says hibernate tools is version 3.3.0v200910281724

the xml hibernate editor does not report required missing elements while the tree validator
for example:
<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.pnx.underwrite.bo.letters" default-cascade="evict,merge,lock" default-access="property" auto-import="true">
<class name="Paragraph" table="underwrite_letter_paragraph" mutable="true" polymorphism="implicit" dynamic-update="false" dynamic-insert="false"
batch-size="10" select-before-update="false" optimistic-lock="version">
<cache usage="read-write" />
<id name="id" type="long" access="property" unsaved-value="-1">
<generator class="native" />
</id>

<property name="text" not-null="false" unique="false" update="true" insert="true" />

<property update="false" access="property" type="timestamp" name="created">
<column name="CREATED" sql-type="date" />
</property>

<property update="true" access="property" type="timestamp" name="modified">
<column name="MODIFIED" sql-type="date" />
</property>

<property update="true" not-null="true" access="property" type="boolean" column="DELETED" name="deleted" />

<set name="templates" access="field" table="underwrite_para_temp" >
<key column="template_Prm_Ref" foreign-key="uw_fk_para"/>
<many-to-many class="Paragraph" column="paragraph_prm_ref"/>
</set>
</class>
</hibernate-mapping>

if i remove the key columns the tree editor will report an error but the xml editor won't.

dito with using entity references with classpath, the tree editor reports an error, while xml does not (and this time the tree editor is wrong off course).